Generally, a duct is an air passage, i.e., a portion of air conditioning equipment which is manufactured as a duct connection tube for ventilation and circulation of air to protect a respiratory organ from interior contaminant materials such as fine dust, carbon dioxide, and harmful bacteria, especially, for a user who uses multi-use facilities such as public facilities, residences, and underground shopping areas.
These ducts become complicated and diversified in their structures due to convenience and design of facilities.
In accordance with the complicated structures of facilities as described above, the duct manufacturers are manufacturing various ducts such as circular ducts, T-shaped ducts, Y-shaped ducts, and elbow-shaped ducts in consideration of the purpose, use position, and size of the duct.
The Patent Document 1 entitled “apparatus and method for manufacturing spiral duct (Korean Patent No. 10-0599078)” discloses a kind of elbow-shaped duct. In this patent document 1, the apparatus for manufacturing a spiral duct includes a first edge forming roll for forming dual bent parts at both straight edges of a metal band, a cutting roll for cutting the metal band extracted from the first edge forming roll in a waved shape by periodically varying a horizontal rotation angle or in a straight shape in its longitudinal direction, and a seaming device for coupling a single bent part with the dual bent part winding the cut metal band in a spiral shape, and thus has an advantages in that since a horizontal rotation angle of a cutting roll is periodically varied to continuously cut a metal band along a straight line and a waved line, it is possible to form a duct in which straight connection ducts are integrally formed with a curved duct.
However, “the apparatus and method for manufacturing spiral duct” of Patent Document 1 are time consuming due to too many duct forming processes, and cannot be worked in a narrow space due to too many components.
Also, the metal band having a plate shape is cut into a straight line and a waved line, respectively, and the straight and waved metal bands are inserted into the seaming device one by one and then wound into a spiral shape to form the straight and waved metal bands into a cylindrical shape and couple the dual bent part and the single bent part into an integral duct. Accordingly, it is impossible to manufacture a duct formed into a cylindrical shape.